(a) Field of the Invention
The present invention relates to a roaming service system for global system for mobile communications (GSM) service subscribers in a code division multiple access (CDMA) service area, a location registering method, a call transmitting and receiving method, and a short message (SM) transmitting and receiving method using the roaming service system. More specifically, the present invention relates to a roaming service system for GSM service subscribers in a CDMA service area, a location registering method, a call transmitting and receiving method, and a SM transmitting and receiving method using the roaming service system when a GSM service subscriber installs a subscriber identity module (SIM) card in a CDMA terminal and receives a roaming service in a CDMA service area.
(b) Description of the Related Art
Recently, as demands for mobile communications have greatly increased, requests for global roaming services that enable telephoning all around the world using a single phone number have multiplied.
When a foreign GSM service subscriber comes to Korea and attempts to receive a CDMA service, the subscriber must borrow a new terminal from an airport lounge or a mobile service agency and obtain a new subscriber number instead of using the subscriber's previous number.
In particular, in the GSM method, the subscriber installs a SIM card that holds the subscriber's profile, in the subscriber's terminal. This mobile communication method using a SIM card enables any subscriber to borrow a SIM-using terminal, install the subscriber's SIM card in the terminal, and use the subscriber's original number in any country where the GSM service is used. However, in Korea, where the CDMA service is provided instead of the GSM method, the GSM subscribers cannot use their original numbers using the SIM cards.
Recently, the countries that use the CDMA method have gradually been attempting to adopt user identity module (UIM) cards similar to the SIM cards to make use of advantages of the SIM cards. Accordingly, CDMA terminals that accommodate the UIM cards are also being developed. The SIM card is identical to the UIM card in its size so it can be installed in the CDMA terminal, but it is impossible to use a CDMA terminal with an installed SIM card and receive the mobile communication service because of differences between the CDMA service method and the GSM service method.